The present invention relates to a method for manufacturing an Alxe2x80x94Nixe2x80x94Fe-series alloy fin material for brazing that has excellent corrosion resistance, mechanical strength, and thermal conductivity. More particularly, the present invention relates to a method for continuously manufacturing an Alxe2x80x94Nixe2x80x94Fe-series alloy rolling coil for fin material, capable of manufacturing fin material having reduced thickness with excellent productivity while improving the characteristics thereof.
Many automotive heat exchangers are made from Al and Al alloys and fabricated by brazing. In general, for brazing, Alxe2x80x94Si-series brazing material is used, and consequently, brazing is carried out at a high temperature of around 600xc2x0 C. Heat exchangers, like radiators, etc., have thin-wall fins (2) machined in a corrugated form among a plurality of flat tubes (1) integrally built as shown in FIG. 1. Both ends of the relevant flat tube (1) are allowed to be open to the space formed by a header (3) and a tank (4), respectively. High-temperature refrigerant is fed to the space on the tank (4) side, through the inside of the flat tube (1), from the space on the other tank side. The refrigerant brought to low temperatures by exchanging heat at the tube (1) and the fin (2) sections, is circulated again.
In recent years, heat exchangers have achieved light weight and small size, and consequently, the heat efficiency of the heat exchanger must be improved, and improvement of heat conductivity of the material is desired. In particular, improving the heat conductivity of the fin material has been investigated, and an alloy fin material whose alloy composition is brought close to that of pure aluminum has been proposed as heat-conducting fins. However, when the wall thickness of the fin is reduced, the fin may collapse at the time of assembling the heat exchanger, or it may be destroyed during use as a heat exchanger, if the mechanical strength of fin is not sufficient. Pure aluminum-series alloy fins have a defect of lacking mechanical strength, and to increase mechanical strength, adding alloying elements, such as Mn, etc., is effective, but in the process for manufacturing heat exchangers, there is a brazing process in which the fins are heated to nearly 600xc2x0 C., causing a problem in that elements added to alloys to improve mechanical strength become solid-soluble again during heating for brazing, and they may block improvement of the heat conductivity.
As fin materials that solve these problems, alloys with Ni and Co added to Alxe2x80x94Sixe2x80x94Fe alloys are proposed, which exhibit characteristics of excellent mechanical strength and heat conductivity (JA-A-7-216485 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application), JP-A-8-104934, etc.).
However, these fin materials need a special fabrication process, as shown in JP-A-9-157807, to secure melting resistance during brazing. In particular, of these fin materials, when they contain more than 1.5% of Fe (% means wt %; the same applies hereinafter), the final cold-rolling ratio must be reduced in order to prevent melting at the time of brazing. This corresponds to Sample No. 7 of the examples of JP-A-9-157087, in which a cold-rolling ratio as low as 9.8% is proposed. That is, carrying out the pass at a low rolling ratio in the industrial rolling of thin-wall aluminum alloy materials, results in difficulty achieving sheet flatness during rolling, causing a problem of being industrially difficult to roll, and a low final cold-rolling ratio causes a problem of difficulty forming corrugates themselves, because mechanical strength difference is too small from the O-material condition.
Furthermore, in aluminum alloys with Fe exceeding 1.5% added together with Ni, an Alxe2x80x94Fexe2x80x94Ni-series intermetallic compound is generated, and these are factors of improving mechanical strength and heat conductivity, but they also cause a problem of lowering the corrosion resistance of the fin material itself. The fin material protects the tube, as a sacrificial corrosion-preventive material, but if the amount of corrosion of the fin material itself is excessively great, the fin is consumed by corrosion in the early stages and is unable to prevent tubes from corrosion over a long time.
In addition, using coils fabricated by casting these alloys by the continuous casting rolling method to manufacture, fin materials has been attempted, but it causes a problem of broken coils midway during cold-rolling it up to the fin materials. Coil breakage during rolling at high speed not only causes a failure to obtain products but also sets fire to oil of the cold-rolling machine, which is dangerous.
The present invention is a method of producing an aluminum alloy fin material for brazing, which comprises:
casting an aluminum alloy by continuous cast-rolling, wherein the aluminum alloy comprises more than 0.1 wt % but 3 wt % or less of Ni, more than 1.5 wt % but 2.2 wt % or less of Fe, and 1.2 wt % or less of Si, and at least one selected from the group consisting of 4 wt % or less of Zn, 0.3 wt % or less of In, and 0.3 wt % or less of Sn, and further comprises, if necessary, at least one selected from the group consisting of 3.0 wt % or less of Co, 0.3 wt % or less of Cr, 0.3 wt % or less of Zr, 0.3 wt % or less of Ti, 1 wt % or less of Cu, 0.3 wt % or less of Mn, and 1 wt % or less of Mg, the balance being unavoidable impurities and aluminum, and
cold-rolling in which annealing at 250 to 500xc2x0 C. is conducted two times or more midway in the cold-rolling process, thereby producing the aluminum alloy fin material of a thickness of 0.10 mm or less;
wherein a cast coil with a thickness of 2.5 mm or more but 9 mm or less is produced by the continuous cast-rolling, and
wherein the second last annealing during the cold-rolling step is carried out with a thickness of 0.4 mm or more but 2 mm or less for the cold-rolled aluminum alloy, and wherein the final annealing is carried out under heating conditions that do not allow complete recrystallization.
Other and further, features, and advantages of the invention will appear more fully from the following description, take in connection with the accompanying drawings.